Lab 1 ELEC 2607

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Carleton University *

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2607

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Electrical Engineering

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Dec 6, 2023

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pdf

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Lab 1 ELEC2607 Glenn Wiliams 1017428012 Lab Section: L3 (8:30 - 11:30AM)

Introduction For this lab we were tasked to build a telephone switch, whose purpose is to connect 1 caller to another. Since many simplifications had to be made the communication on this telephone switch will be 1 way only, with the person on the receiving end only being able to listen. These types of circuits are commonly used in communication systems to transfer data signals using a single line transmission. The telephone switch being built in the lab is also a common system used by telephone solicitors to connect 4 callers to 8 receivers. The telephone switch consists of a 4 input multiplexer and 8 output demultiplexer which are connected by a trunk line. In simple terms the 4 input multiplexer is a circuit which is used to select 1 of the 4 inputs and then it takes this input and it sends it to the output through the trunk line. The 8 output demultiplexer is also a circuit, however instead of taking in inputs, it takes in outputs, which are sent from the multiplexer circuit in the form of digital signals. The demultiplexer then converts these digital signals to their original form; in a real telephone circuit these signals would have been converted to audio. However, since there is no microphone and no audio to digital converters, this telephone switch will only be able to take in signals by flicking a switch on and off very fast, essentially acting like a morse code transmitter, and therefore the outputs will just be the inputs of the switch. This circuit was built using a program called Multisim, which allows students to make various circuits and test them in the program. For the testing section “INTERACTIVE_DIGITAL_CONSTANT” will be used to take in inputs, it basically acts like a switch because it only has 1 or 0 as the outputs. For the output testing “PROBE_DIG” will be used, which is essentially an LED, which will receive the input signals. The remainder of the report will further delve into more details about the lab through the specifications, design, implementation and testing sections. Specifications This specific design was built in the previous years, however due to current circumstances this design had to be simulated using NI MultiSim. The telephone switch made in the lab consists of a 4 input MUX, and an 8 output DEMUX, since we were not taught how to make audio to digital converters a simple switch had to be used. Now the circuit uses a switch, and only 2 inputs are possible, making the circuit operate on binary “1” or “0”. For the outputs LEDs were used so the only 2 possible outputs are “ON” or “OFF”. The switches for this lab are virtual switches called “INTERACTIVE_DIGITAL_CONSTANT” which act like a real life switch which has values 0 and 1, for ON and OFF, it is possible to change these outputs to test the design with different values. The way to test outputs for this design was to use “PROBE_DIG_color”, these probes have different colours to pick from, and

when the circuit receives an input and everything goes through the system, these probes will light up, or turn off depending on the inputs. For this design there were specific requirements which needed to be met. The circuit was only supposed to use NAND/NOR/NOT gates. This did not really limit the functionality of the telephone switch in any way, however, it made it more complex to construct as the signals need to be inverted multiple times when passing through the NAND/NOR gates, which makes room for mistakes. There is however not a limit to the amount of gates used, because the MUX and DEMUX can be conjoined to make room for more inputs and outputs. This design is pretty good although it is limited by some factors. The size of it in real life and not just on a simulated program would be way too tiny to be used efficiently, unless design changes are made to accommodate it. For the power aspect of it, it should not be a problem at all because the circuit is tiny and could be powered by a small battery, power only becomes an issue once there are more MUX and DEMUX circuits being used in one design. For time limit there is a small issue, in order to maximize the amount of callers that can use the system per day, an automatic time limit switch will need to be added in order to allow more users to make calls. Design The Design process for this circuit was quite lengthy, firstly the prelab had questions that would support in the designing of the circuit. The first question that helped with the design of the Lab was question 1.8, which gave components and asked to turn them into a 2 - input MUX. It was created with 2 AND gates 2 NOT gates and 1 NOR GATE. Although in the lab itself it was asked to build all of the circuits using NAND,NOR,NOT gates this question helped with the general understanding of how a 4 input mux could be created The MUX created in the prelab question 1.8 can be seen down below in figure [1] Figure [1] Pre-Lab question 1.8, 2 - input MUX

The next step in the design was to understand how to partition a 4 input 8 output phone switch into one 4 input MUX, one 2 output DEMUX, and two 4 output DEMUXs. This step was essential as it showed how the phone circuit is broken down. By doing this step, it explained how the final phone switch circuit would be designed, and it broke it down further into how an 8 output DEMUX could be made by linking one 2 output DEMUX and two 4 output DEMUXs. The figure [2] down below shows question 1.10 from the pre-lab and shows how a 4 input MUX and an 8 output DEMUX can be partitioned into one 4 input MUX, one 2 output DEMUX and two 4 output DEMUXs. Figure [2] Pre-Lab question 1.10, 4 input MUX 8 output DEMUX partitioned. The figure above shows how the DEMUX takes in 4 inputs with each respective one representing a caller, and 8 output sections which would be the receivers, and T representing the trunk line, which links the MUX and DEMUXes together. After designing the above figure, the next question 1.11 asked to partition a 4 output DEMUX into three 2 output DEMUXs. This step broke down how a 4 - output DEMUX can be made from three 2 output DEMUXs. This step was another stepping stone for the lab as it showed how the 4 output DEMUX could be further broken down into each individual component. And this knowledge also helped with understanding how a 4 input demux could be partitioned. The following figure [3] shows how a 4 output DEMUX can be turned into three 2 output DEMUXs

Figure[3] Pre-Lab question 1.11, three 2 output DEMUXS turned into a 4 output DEMUX. The above figure is a simplification made using trapezoidal symbols, in reality this 4 output DEMUX is a culmination of NANDs NOTs and NORs gates. Next part of the process is the actual construction of the telephone switch, using the MultiSim program. In question 4 of the lab it is asked to design a 4 input MUX, using the knowledge of how a 2 input MUX circuit is constructed from question 1.8 figure [8], we can construct a 2 input MUX circuit. From then on we use the knowledge obtained in question 1.11, so now it is known that one must use 3 of the same MUX circuits to create a 4 input MUX. The user then links the 3 MUX circuits together and tests the outputs to make sure everything is running fine. The complete MUX circuit contains 6 NANDs, 12 NOTs, and 3 NORs. The following figure [4] shows how a 4 input MUX can be made.

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